1. Field of the Invention
The present invention relates to a stabilizing agent for beer comprising particular amorphous silica and, more specifically, to a stabilizing agent for beer comprising amorphous silica that exhibits a large negative zeta-potential in the pH region of the beer.
2. Prior Art
Beer is a transparent alcoholic beverage exhibiting shiny amber color and is a fermentation product obtained by fermenting the malt of barley and hop as main starting materials and recovering the product therefrom. In addition to taste, fragrance and flavor as an alcoholic beverage, therefore, appearance also serves as an important factor that determines commercial value.
When the beer is preserved for extended periods of time being bottled, canned or contained in barrels and when it is chilled to drink, there often takes place haze phenomenon in which dregs and haze occurs in the beer and the beer becomes turbid. The beer which occurs haze is regarded to be the one that has poor durability and is not, therefore, appreciated and besides lacks commercial value of the beer.
The haze can be divided into three cases; i.e., cold haze, permanent haze and freeze haze. It has been reported that the beer contains cold haze in an amount of from 1.4 to 8.1 mg/l and permanent haze in an amount of from 6.6 to 14.1 mg/l. It has also been reported that the haze occurs in the order of from 44 to 100 mg/l.
The cold haze occurs when the beer is chilled at about 0.degree. C. and dissolves again at a temperature of 20.degree. C. The permanent haze is also called oxidized haze but does not dissolve again. The freeze haze occurs when the beer is frozen or is chilled to about -5.degree. C. which is close to freezing.
It has been said that the beer becomes turbid when part of proteins derived from the barley and hop that are the starting materials and soluble components such as polyphenol and the like become insoluble or when these colloidal components associate with each other.
In this specification, the components which are dissolved in the beer or are decomposed therein in a colloidal form and become causes of turbidity when the beer is preserved for extended periods of time or is chilled, are referred to as turbidity precursors.
As described above, haze in the beer stems from the turbidity precursors that ubiquitously exist in the beer and as far as the turbidity precursors remain in the beer, occurrence of haze cannot be extinguished though it may vary depending upon the conditions at that time.
Therefore, a variety of methods (stabilizing treatments) have been put into practice for preventing the beer from becoming turbid and efforts have been made to prevent the beer from degenerating and to improve durability by removing the turbidity precursors remaining in the beer applying various methods and technologies.
Turbidity precursors have heretofore been separated and removed by adding to the beer such haze preventing agents as papain (vegetable albumin decomposing enzyme recovered from papaia), tannic acid, polyvinyl pyrrolidone, silica gel, etc.
In particular, the silica gel has been extensively used as a stabilizing agent since it little affects the quality of the beer such as, fragrance, taste, favor, froth and the like.
As the silica gel (amorphous silica) for stabilizing the beer, it has heretofore been known to use a hydrogel or a xerogel. Japanese Patent Publication No. 61914/1988 discloses the use of silica hydrogel particles having a water content of 60 to 90% by weight and a BET specific surface area of not smaller than 300 m.sup.2 /g obtained by the reaction of an acidic silica sol with sodium silicate in the presence of an aqueous solution of salts, for stabilizing the beer.
Japanese Patent Publication No. 27483/1991 discloses a water-containing gel for stabilizing the beer having a specific surface area of from 530 to 720 m.sup.2 /g, a porous volume of from 0.9 to 1.5 ml/g, an average porous diameter of from 50 to 120 angstroms, a water content of from 7 to 25% and a pH of from 6.0 to 8.0 when it is suspended in the water at a concentration of 5%.
Moreover, Japanese Patent Publication No. 38188/1988 discloses a method of treating beer by bringing a fired silica xerogel into contact with the beer, the fired silica xerogel having a surface area over a range of from 100 m.sup.2 /g to 450 m.sup.2 /g, a porous volume of at least 0.66 cc/g, an average porous diameter of not smaller than 100 angstroms, exhibiting a peak at 3760 cm.sup.-1 in the infrared-ray spectrum indicting the presence of a single surface silanol group, and exhibiting a ratio of absorbance at 3760 cm.sup.-1 to the absorbance at 1890 cm.sup.-1 of not smaller than 2.2, and then separating the silica from the beer.
According to the above-mentioned method of using the silica hydrogel or the water-containing gel, microorganisms such as molds often proliferate during the production of the gel, during the preservation or during the transit. When an acid is added to the gel to prevent the proliferation, however, the acid often infiltrates into the beer.
The latter method of using the fired xerogel which is one of the above-mentioned prior methods is meaningful from the standpoint of eliminating inconveniences of when the hydrogel or the water-containing gel is used. According to the study by the present inventors, however, it was learned that an infrared absorption peak at a wave number of 3760 cm.sup.-1 is specific to the type-A silica gel having a very large specific surface area but the type-B silica gel used in the present invention does not at all exhibit the above infrared absorption peak.